Series Is Presented Here As Two Variables--(1)--Seasonally Adjusted Data, Quarterly, 1946-1960 (2)--Seasonally Adjusted Data, Monthly, 1955-1964. Source: U.S. Bureau Of The Census; Originally From The American Trucking Association, Department Of Research And Transport Economics.
This NBER data series q03032 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: q03032
Release: NBER Macrohistory Database
National Bureau of Economic Research, Index of Truck Tonnage for General Freight Carriers for United States [Q03032USQ350SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q03032USQ350SNBR, June 1, 2016.